Manufacture of composite pistons



T. P. CHASE MANUFAGTURE 0F COMPOSITE PIsToNs Jan.` 7, 1936.

original Filed April 15, 1929 Patented Jan. 7, 1936 PATENT OFFICE 2,026,612 MANUFAOTURE OF COMPOSITE Pls'roNs Theron P. Chase, Detroit, Mich., assigner, by

mesne assignments, to General Motors Corporation, Detroit, Mich., a corporation of Delaware Original application April 15, 1929, Serial No.

355,269. Divided and this application September 15, 1932, Serial No. 633,254

1 claim.

This invention relates to composite pistons. This application is a division of my co-pending application S. N. 355,269 which was led on April 15, 1929. v

By .the term composite piston is meant a piston whose head or bodyV is made of a light metal or alloy, such vas aluminum or an alloy of aluminum, and Whose skirt or cylinder wall bearing surfaces are made of a harder, wear-resisting metal, such as iron or steel.

On account of the diierence between the temperature coeflicients of expansion of the metals or alloys of which the head or body and the skirt or cylinder wall bearing surfaces of such pistons are made, in composite pistons as heretofore constructed, there has been either (1) a tendency for the parts to become looseand rattle at ordinary atmospheric temperatures, or (2) a tendency for the piston to bind in the cylinder at ordinary operating temperatures. It is the principal object of this invention to provide a method of producing a composite piston whose parts will not become'loose and rattle at ordinary atmospheric temperatures and which will not bind in the cylinder at ordinary Operating temperatures. For a more complete understanding of the nature and the objects of my invention, reference is made to the following specication, wherein the invention is described with reference to the accompanying drawing in which there is shown a piston made in accordance withvthe invention.

In the accompanying drawing:

Fig. 1 is a longitudinal cross-section through the piston in a, plane at a right angle to the axis of the wrist pin bosses.

Fig. 2 is a section taken on the line Fig. 1.

Fig. 3 is a section taken on the line 3--3 of- Fig. 1.

Fig. 4 is a longitudinal cross-section, through the skirt or bearing sleeve of the piston, taken in a plane at a right angle to the axis of the wrist pin openings.

Fig. 5 is an enlarged fragmentary section, taken on the line 5-5 of Fig. 3.and showing, on an exaggerated scale, the space between the skirt or bearing sleeve and the body of the pistonat ordinary atmospheric temperatures. n

In the accompanying drawing, the reference character `.5,indicates the skirt or bearing sleeve of the piston, and the reference character 6 a ring circumferentially secured, preferably by welding, to the-interior of the skirt or bearing sleeve intermediate its ends. The skirt or bearing sleeve 5 is preferably made of high carbon l steel and the ring of any suitable material, such as steel. There are provided in the skirt or ,bearing sleeve, intermediate its ends, diametrically opposed openings 1, and on the ring '6, intermediate the openings 1,' a plurality of substantially horizontally` disposed, inwardly extending prongs '8.

' The body of the piston is made of a light metal or alloy, such as aluminum or an alloy of alumiinwardly extending wrist pin bosses Il ythroughy which extend openings l2 which are coaxial with the openings 1 in the skirt vor bearing sleeve. 'I'he body and the skirt or bearing sleeve are secured together by means of the prongs 8 which are embedded in the thickened portion of the lower end of the `annular wall portion I0.

The skirt or bearing sleeve 5 may be formed by any suitable process and the ring 6 is preferably secured thereto by welding. To complete the piston, the skirt or-bearing sleeve is placed in a suitable mold-preferably a permanent mold-and the mold and skirt or bearing sleeve heated to such a temperature that, when the fcient pressure radially against the skirt or bearing sleeve to expand it to a diameter greater than that which it would normally assume at that temperature. After the mold and the skirt or bearing sleeve have been heated to the desired temperature, the molten metal of which the body is to be formed, is introduced into the mold, and thus the body portion is formed and becomes interlocked with the skirt or bearing sleeve 5 by the prongs 8 which become embedded in the metal of the head.

By heating the skirt or bearing sleeve 5to the temperature mentioned above, before the molten metal of which the'body is to be formed is cast thereinto, it is insured that, when the piston is .at ordinary engine operating temperatures, there cylinder. At lower temperatures, such as those at which the piston operates when the engine is being started from the cold, the body will tend to withdraw radially from the skirt or bearing sleeve by sliding inwardly on the prongs 8 on the ring 6, The provision of a plurality of these prongs 8, each of which enters the body at a different angle, prevents the body and the skirt or bearing sleeve from becoming loose and rattling under such conditions.

When the engine in which the piston is used is first started, the body will become heated very quickly and will, therefore, expand quickly until it is in circumferential contact with the skirt or bearing sleeve, for until the body' and skirt are in circumferential contact the rate of heat transfer betweenthe body and skirt or bearing sleeve is obviously quite low. This feature is a Ihighly desirable one since it is thereby insured that for no great length of time, while the engine is operating, will the prongs .8 be required to function as the sole connecting means between way of limitation, and that the scope of my invention is to be determinedonly by the appended claim.

That method of forming a composite piston which includes, producing a skirt or bearing sleeve of a wear resisting metal having a relatively low temperature coeflicient of expansion, securing to the skirt or bearing sleeve interiorly thereof and between its ends a ring on which there are provided substantially horizontal, inwardly directed projections, heating the skirt or bearing sleeve andthe ring to such a temperature that the outer surface of the head or body will contact lightly circumferentially with the inner surface of the skirt or bearing sleeve and the inner surface of' the ring when the piston cools to ordinary engine operating temperatures, and casting into the interior of the skirt or bearing sleeve and the ring While they'are at the mentioned tempera- 20 THERO NP. cfs E. 25 

